Internal combustion engines on the basis of Otto (gasoline) engines are generally operated with fuel from hydrocarbons produced from fossil fuels based on refined crude oil. Ethanol produced from renewable resources (plants) or another kind of alcohol is increasingly being added in various mixing ratios to the fuel. In the USA and Europe a mixture of 75-85% ethanol and 15-25% gasoline is often distributed under the trade name E85. The internal combustion engines are designed in such a way that they can be operated with pure gasoline as well as with mixtures up to E85. This is denoted as a “flex-fuel operation”. The operating parameters in the flex-fuel operation have to be adapted in each case to the existing fuel mixture for an efficient operation with only a small discharge of toxic emissions; while at the same time high engine performance is guaranteed. A stoichiometric fuel-air mixture ratio is, for example, present at 14.7 parts of air per part of gasoline; however, when using pure ethanol, a proportion of air of 9 parts must be set.
The taking of the fuel, which has ingressed into the engine oil during cold starting, into account as well as the fuel evaporating out of the engine oil at high temperatures has to fundamentally take place with all internal combustion engines; however, is mainly employed with Otto (gasoline) engines with a flex-fuel-mode of operation.
Ethanol and gasoline have different evaporation properties. Ethanol evaporates at a lower temperature to a lesser degree than gasoline, so that more ethanol has to be metered in during cold starting than is the case for gasoline. This leads to the fact that when cold starting with ethanol and during the subsequent warm-up phase, considerably more fuel is wiped from the cylinder walls into the engine oil via the piston rings. When the temperature of the engine oil increases, this fuel evaporates and is added via the crankcase ventilation system to the fresh air supply provided to the engine. The total amount of fuel situated in the engine oil is only expelled during extended warm-up phases. The additional richening of the mixture caused by the evaporated fuel has to be taken into account. Especially during low load-rotational speed-conditions, this richening can be significant. The richening of the fuel mixture can be taken into account by the closed-loop lambda control at certain percentages. This can, however, be insufficient in certain cases and can at the least lead to drivability problems during a dynamic operation mode.
A first beginning for improving the aforementioned problem is according to the technical field to track the number of cold starts and to gradually reset this counter in the warm-up phases. If the cold start counter exceeds a predetermined value and if the temperature of the engine oil exceeds a typical value of 70EC to 90EC for the outgassing, the lambda controller will be decontrolled in a range expanded to small values in order to take into account the proportion of the fuel, which has evaporated out of the engine oil.
In a document of the applicant (reference number: DE 102004008891.8), it is additionally proposed to model the mass flow of the fuel outgassing from the engine oil and to take said mass flow into account as a pilot control value when calculating the quantity of fuel to be metered. Especially among other things the quantity of fuel collected in the engine oil, the composition of the fuel as well as the temperature history and the current temperature of the engine oil are included in the fuel mass flow determined from the model. The modeling described prevents deviations of the composition of the fuel/air mixture; however, not in all desired operating conditions and partially not with the desired accuracy.
In the U.S. Pat. No. 5,331,940, a device and a method for taking the outgassing of fuel into account from the engine oil of an internal combustion engine with a positive crankcase ventilation are described. The positive crankcase ventilation thereby carries a portion of the intake air flow over the camshaft housing and the crankcase housing and can, depending on the operating state of the internal combustion engine, via a valve variably controlled add this intake air flow to the to the fresh air supply before the fuel metering. In a first step, a nominal quantity of injected fuel is determined from a quantity of fresh air supplied to the internal combustion engine and the engine's rotational speed. If it is detected by means of a least deviation of the lambda value of the exhaust gas of the internal combustion engine from its nominal value that an outgassing of fuel from the engine oil is to be taken into account, an expected quantity of outgassing is determined from a characteristic diagram plotted versus engine rotational speed and nominal quantity of fuel injected while taking into account the time function. The characteristic diagram is corrected by evaluating a deviation, which still remains, of the lambda value from the nominal value.
It is the task of the invention to provide a method, which allows for an improved way of taking the outgassing of fuel from the engine oil of an internal combustion engine into account and which balances the control deviation of the lambda controller.